Fluorine Gas Generation Apparatus

ABSTRACT

A fluorine gas generating device comprises an electrolytic tank that generates at an anode side a main-product containing as a main component fluorine gas and at a cathode side a by-product gas containing as a main component hydrogen gas by subjecting, in an electrolytic bath, hydrogen fluoride in a molten salt containing therein hydrogen fluoride to an electrolysis; a hydrogen fluoride supply source that stores therein hydrogen fluoride that is to be fed to the electrolytic tank to fill up hydrogen fluoride; a hydrogen fluoride supply passage through which hydrogen fluoride flows from the hydrogen fluoride supply source to the electrolytic tank; and a vaporizer that is connected to the hydrogen fluoride supply passage to vaporize hydrogen fluoride supplied from the hydrogen fluoride supply source.

INDUSTRIAL FIELD

The present invention relates to fluorine gas generating devices of a type that is able to stably supply a fluorine gas.

TECHNICAL BACKGROUND

Hitherto, there has been known a fluorine gas generating to device that comprises an electrolytic tank which electrolyzes hydrogen fluoride in an electrolytic bath that includes a molten salt containing therein hydrogen fluoride and which generates at an anode side thereof a main-product gas that contains as a main component fluorine gas and at a cathode side thereof a by-product gas that contains as a main component hydrogen gas (Patent Documents 1 and 2).

When, in fluorine gas generating devices of such type, a fluid level of the molten salt lowers due to the electrolysis of hydrogen fluoride in the electrolytic bath, hydrogen fluoride is directly fed into the electrolytic bath through a hydrogen fluoride supply passage, from the outside of the electrolytic tank, using a hydrogen fluoride supply source such as a hydrogen fluoride cylinder bottle, a hydrogen fluoride tank or the like.

When, in the fluorine gas generating device, fluorine is largely produced, the fluid level of the electrolytic tank lowers since the fluid level at the anode side where fluorine gas is produced is affected by the amount of fluorine gas produced by the fluorine gas generating device.

Fluorine gas has a high reactivity, and thus, when the fluid level of the electrolytic tank largely changes, there is such a possibility that fluorine gas and hydrogen gas become mixed to induce a reaction therebetween. Thus, it is important to keep the fluid level of the electrolytic tank at a constant level for suppressing undesired influence to the quantity of generation of fluorine gas. Accordingly, for keeping the fluid level of the electrolytic tank at a constant level, it is necessary to stably feed a sufficient amount of hydrogen fluoride to the tank.

In the fluorine gas generating device disclosed in Patent Documents 1 and 2, feeding the electrolyte tank with hydrogen fluoride is so made that the hydrogen fluoride supply source is directly heated by a heater or the like and hydrogen fluoride kept in a gaseous condition is fed to the tank through the hydrogen fluoride supply passage.

PRIOR ART DOCUMENTS Patent Documents

-   [Patent Document 1] Japanese Laid-open Patent Application (tokkai)     2004-43885 -   [Patent Document 2] Japanese Laid-open Patent Application (tokkai)     2009-242944

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

When, in the conventional method, fluorine is generated in large quantity, it is impossible to feed the electrolytic tank with a sufficient amount of hydrogen fluoride to keep the fluid level of the tank at a constant level, and thus it tends to occur that feeding the tank with hydrogen fluoride is unstable. As a result, the fluid level of the electrolytic tank easily changes, so that stable generation of fluorine gas is difficult.

In the method of using the cylinder bottle, frequent exchange of hydrogen fluoride cylinder bottles for increasing the amount of hydrogen fluoride fed to the tank may be thought out. However, if such frequent exchange is carried out, lowering in productivity due to a temporary haft of the device as well as increase in work load due to load increase by exchange of cylinder bottles are induced.

For feeding the tank with hydrogen fluoride, there may be a method in which, with usage of a large-sized hydrogen fluoride tank, the hydrogen fluoride tank is directly heated, so that gaseous hydrogen fluoride is led into the electrolytic tank. However, in this method, because of the size enlargement of the hydrogen fluoride tank, the facilities for heating the hydrogen fluoride tank become large and running cost is increased.

Furthermore, in the conventional method, in case of using a large-sized hydrogen fluoride tank, the passage through which the gaseous hydrogen fluoride flows is increased in length, so that when a large amount of gaseous hydrogen fluoride is suddenly led into the passage from the hydrogen fluoride supply source, heating of the gaseous hydrogen fluoride in the passage is not sufficiently carried out inducing a possibility of liquefaction of hydrogen fluoride, which tends to cause the liquefied hydrogen fluoride led into the electrolytic tank to make a sudden boiling thereof bringing about a fluctuation of the fluid level of the electrolytic tank.

The present invention is provided by taking the above-mentioned problems into consideration and aims to provide a fluorine gas generating device that is able to stably carry out feeding of hydrogen fluoride to an electrolytic tank even when a large amount of fluorine gas is produced.

Means for Solving the Problems

In order to solve the above-mentioned problems, the inventors have carried out serious studying for finding the way for solving the above-mentioned problems and finally found out a fact, viz., the concept of the present invention in which when, beside the hydrogen fluoride supply source, a vaporizer is mounted to the hydrogen fluoride supply passage for receiving and vaporizing the liquefied hydrogen fluoride fed from the hydrogen fluoride supply source, feeding of hydrogen fluoride to the electrolytic tank becomes stable.

That is, in accordance with the present invention, there is provided a fluorine gas generating device that generates fluorine gas by subjecting hydrogen fluoride in a molten salt containing therein hydrogen fluoride to an electrolysis, the fluorine gas generating device being characterized by an electrolytic tank that generates at an anode side a main-product containing as a main component fluorine gas and at a cathode side a by-product gas containing as a main component hydrogen gas by subjecting, in an electrolytic bath, hydrogen fluoride in a molten salt containing therein hydrogen fluoride to an electrolysis, a hydrogen fluoride supply source that stores therein hydrogen fluoride that is to be fed to the electrolytic tank to fill up hydrogen fluoride, a hydrogen fluoride supply passage through which hydrogen fluoride flows from the hydrogen fluoride supply source to the electrolytic tank and a vaporizer that is connected to the hydrogen fluoride supply passage to vaporize hydrogen fluoride supplied from the hydrogen fluoride supply source.

In accordance with the present invention, the fluorine gas generating device may have such a feature that the vaporizer comprises a hollow vessel that is equipped with a temperature adjuster and has therein a vaporizing chamber, a hydrogen fluoride inlet portion that introduces thereinto liquefied hydrogen fluoride from the hydrogen fluoride supply source, and a hydrogen fluoride outlet portion that discharges gaseous hydrogen fluoride from the vaporizing chamber.

In accordance with the present invention, the fluorine gas generating device may further comprise a flow rate control valve that controls a flow rate of hydrogen fluoride led into the vaporizer, a fluid level detecting means that detects a fluid level of hydrogen fluoride contained in the vaporizer and a control means that, in accordance with a detected output from the fluid level detecting means, controls an open degree of the flow rate control valve in such a manner as to cause the fluid level of hydrogen fluoride in the vaporizer to take a given level.

In accordance with the construction of the invention, controlling of the fluid level of hydrogen fluoride in the vaporizer is facilitated and thus, supplying of hydrogen fluoride is much stably carried out.

If desired, by the aid of the control means, supplying of hydrogen fluoride from the hydrogen fluoride supply source may be so made that the fluid level of hydrogen fluoride in the vaporizer keeps a given level constantly.

Advantages of the Invention

In the present invention, a vaporizer is connected to a hydrogen fluoride supply passage for vaporizing liquefied hydrogen fluoride and the amount of hydrogen fluoride received in the vaporizer is adjusted. Accordingly, even when, due to a large generation of fluorine gas by the electrolytic tank, it becomes needed to feed the electrolytic tank with a large amount of hydrogen fluoride, it never occurs that the amount of hydrogen fluoride fed to the tank shows a shortage. Accordingly, feeding of hydrogen fluoride to the tank is stable and thus undesired fluctuation of the fluid level is suppressed, which brings about a stable supply of fluorine gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of a fluorine gas generating device that embodies the present invention.

FIG. 2 is a schematic view of a vaporizer used in the invention.

FIG. 3 is a drawing showing one example of a fluorine gas generating device that mounts both a vaporizer and an electrolytic tank in a common housing.

BEST MODE FOR EMBODYING THE INVENTION

In the following, embodiments of the present invention will be described with reference to the accompanying drawings. A fluorine gas generating device 100 of an embodiment of the present invention will be described with the aid of FIG. 1.

The fluorine gas generating device 100 is a device that generates fluorine gas by subjecting a molten salt containing therein hydrogen fluoride to an electrolysis and supplies fluorine gas thus generated to an external device. As the external device, is a semiconductor production device is exemplified. In such case, fluorine gas supplied is used as a cleaning gas in a semiconductor production process.

The fluorine gas generating device 100 comprises an electrolytic tank 1 that produces fluorine gas with the aid of electrolysis, a fluorine gas feeding system 2 that feeds fluorine gas produced by electrolytic tank to an external device 4 and a by-product gas treatment system that treats a by-product gas produced together with fluorine gas.

First, the electrolytic tank 1 will be described. Within the electrolytic tank 1, there is stored a molten salt that contains therein hydrogen fluoride (HF). By changing the composition of the molten salt stored in the electrolytic tank 1, the composition of fluorine compound gas produced by the electrolytic tank 1 can be suitably changed. As the molten salt, there is used a composition represented by general formula “KF·nHF (n=0.5 to 5.0). For example, in case of using NH₄F·HF molten salt, molten salt, nitrogen trifluoride (NF₃) is obtained, and in case of using NK₄F·KF·HF molten salt, mixture of F₂ and NF₃ is obtained. In the following, an embodiment of the present invention will be described in case of casing a mixed molten salt (KF·2HF) of hydrogen fluoride and potassium fluoride as the molten salt.

An interior of the electrolytic tank 1 is partitioned into an anode chamber 11 and a cathode chamber 12 by a partition wall 6 immersed in the molten salt. In the anode and cathode chambers 11 and 12, there are respectively arranged anode and cathode 7 and 8 that are immersed in the molten salt. By applying a current between the anode and cathode 7 and 8 from an electric power source, there are produced at the anode 7 a main-product gas that contains as a main component fluorine gas (F₂) and at the cathode 8 a by-product that contains as a main component hydrogen gas (H₂). As the anode 7, there is used for is example a carbon electrode, and as the cathode 8, there is used for example soft-iron, Monel or nickel.

Above the fluid level of the molten salt in the electrolytic tank 1, there are defined a first gas chamber 11 a into which fluorine gas produced at the anode 7 is led and a second gas chamber 12 a into which hydrogen gas produced at the cathode 8 is led, the two gas chambers being isolated from each other by the partition wall 6 so that the two chambers don't permit gas transfer therebetween. As is mentioned in the above, for preventing a reaction that would be caused by mixing between fluorine gas and hydrogen gas, the first and second gas chambers 11 a and 12 a are completely separated by the partition wall 6. While, the molten salt contained in the anode chamber 11 and the molten salt contained in the cathode chamber 12 are connected to each other below the partition wall 6.

The melting point of KF·2HF is 71.7° C. and thus it is preferable to control the temperature of the molten salt in the range of 91 to 93° C. To both fluorine gas and hydrogen gas respectively produced at the anode 7 and cathode 8, there is led hydrogen fluoride from the molten salt by an amount corresponding to a vapor pressure of it. Thus, fluorine gas produced at the anode 7 and led into the first gas chamber 11 a and hydrogen gas produced at the cathode 8 and led into the second gas chamber 12 a contain hydrogen fluoride gas therein respectively.

In the following, the fluorine gas supply system 2 will be described. To the first gas chamber 11 a, there is connected a to first main passage 15 through which fluorine gas is led to the external device 4.

To the first main passage 15, there is connected a first pump 17 by which fluorine gas is led from the first gas chamber 11 a for its conveyance. As the first pump 17, a volume-type pump, such as bellows pump, diaphragm pump or the like is used. To the first main passage 15 at a position upstream of the first pump 17, there is connected a refining device 20 that collects hydrogen fluoride mixed with fluorine gas to refine fluorine gas.

In the following, the by-product gas processing system 3 will be described. To the second gas chamber 12 a, there is connected a second main passage 30 that discharges hydrogen gas to the outside.

To the second main passage 30, there is connected a second pump 31 by which hydrogen gas is led from the second gas chamber 12 a for its conveyance. To the second main passage 30 at a position downstream of the second pump 31, there is connected a harmful matter remover 34, so that hydrogen gas conveyed by the second pump 31 is subjected, at the harmful matter remover 34, to an adsorption removing of hydrogen fluoride to be rendered harmless and discharged to the outside.

The fluorine gas generating device 100 has further a material supply system 5 that, for supplementation, feeds the molten salt in the electrolytic tank 1 with hydrogen fluoride as a material of fluorine gas to be produced. In the following, the material supply system 5 will be described.

The electrolytic tank 1 is connected through a material supply passage 41 to a hydrogen fluoride supply source 40 that stores hydrogen fluoride for supplementation of hydrogen fluoride in the tank. The hydrogen fluoride stored in the hydrogen fluoride supply source 40 is fed to the molten salt in the electrolytic tank 1 through the material supply passage 41. If desired, the material supply passage 41 may be provided with a flow rate control valve 71 that controls a feeding flow rate of is hydrogen fluoride. To the material supply passage 41, there is connected a vaporizer 60 that vaporizes liquid hydrogen fluoride fed from the hydrogen fluoride supply source 40. Hydrogen fluoride gas discharged from the vaporizer 60 is kept in a gaseous state by a heating means (not shown) such as heater or the like connected to the material supply passage 41. The vaporizer 60 will be described in detail hereinafter.

To the material supply passage 41, there is connected a carrier gas supply passage 46 through which a carrier gas supplied by a carrier gas supply source 45 is led into the material supply passage 41. The carrier gas is a gas used for guiding hydrogen fluoride from the hydrogen fluoride supply source 40 into the molten salt, and thus, as the carrier gas, nitrogen gas that is an inert gas is used. The nitrogen gas is fed together with hydrogen fluoride to the molten salt in the cathode chamber 12, but the nitrogen gas hardly dissolves in the molten salt and the gas is discharged from the second gas chamber 12 a through the second main passage 30.

In the following, the vaporizer 60 will be described. The vaporizer 60 is a device that receives and vaporizes the liquid hydrogen fluoride fed from the hydrogen fluoride supply source 40 and discharge the gaseous hydrogen fluoride to a given portion. In the following, with the aid of FIG. 2, the vaporizer 60 will be described in detail. It is however to be noted that the vaporizer 60 used in the invention is not limited to a vaporizer that will be described in the following.

As is shown in FIG. 2, the vaporizer 60 is equipped with a temperature adjusting device 64 such as a heater or the like, and comprises a hollow vessel 61 that forms therein a vaporizing chamber 65, a hydrogen fluoride inlet portion 62 that introduces thereinto liquefied hydrogen fluoride from the hydrogen fluoride supply source 40, and hydrogen fluoride outlet portion 63 that discharges gaseous hydrogen fluoride from the vaporizing chamber.

The vaporizing chamber 65 is provided, on its inner wall, with a plurality of projections 66 such as fins or the like for the purpose of achieving an effective heat transmission from the temperature adjusting device 64 to the chamber 65. Although the shape of the projections 66 has no limitation, it is preferable that as is shown in FIG. 2, the projections are shaped like plates and projected at right angles from the wall surface toward the vaporizing chamber 65 throughout the entire surface of the wall. Furthermore, preferably, the projections are placed in the vicinity of the hydrogen fluoride inlet portion 62.

To the vaporizer 60, there is connected a fluid level detecting means that detects the fluid level of the liquefied hydrogen fluoride received in the vaporizing chamber 65. As the fluid level detecting means, a pressure detecting device 68 that detects the pressure in the vaporizing chamber 65 and a fluid level detecting device 69 that detects the fluid level of the liquefied hydrogen fluoride received in the vaporizing chamber 65 are usable. As the fluid level detecting device 69, a level indicator for general purpose use is usable. In this case, the level indicator is inserted in an inserting tube 67 for its purpose. Furthermore, if desired, a thermometer may be connected to the vaporizer 60 for measuring the temperature of the vaporizing chamber 65.

The fluid level of the liquefied hydrogen fluoride in the to vaporizing chamber 65 is so adjusted that the hydrogen fluoride in the chamber keeps an amount in a given range. By keeping the fluid level of hydrogen fluoride in the vaporizing chamber 65 within a given range, the fluorine gas generating device 100 of the present invention generates, at the electrolytic tank, a large amount of fluorine gas, and even when it becomes needed to supply a large amount of hydrogen fluoride to the tank, a needed amount of hydrogen fluoride can be instantly supplied to the tank from the hydrogen fluoride supply source 40, and thus, shortage of amount of hydrogen fluoride to be supplied to the tank never occurs.

For keeping the fluid level of hydrogen fluoride within the given range, some methods are used, one being a method (viz., batch method) in which at first, upper and lower limits of the fluid level are set and when the fluid level of hydrogen fluoride comes to the lower limit, hydraulic fluoride is intermittently fed to the tank, the other being a method (viz., continuous method) in which hydrogen fluoride is continuously fed to the tank in such a manner as to constantly keep the fluid level at a given level.

For keeping the fluid level of hydrogen fluoride within a given range, it is preferable to adjust the fluid level of hydrogen fluoride in the vaporizing chamber 60 based on the results of detection by the fluid level detecting means.

More specifically, as is shown in FIG. 1, as the fluid level detecting means, it is preferable to use the pressure detecting device 68. To the pressure detecting device 68, there is connected a controller 70 (control means), so that detecting results of the pressure detecting device 68 are fed to the controller 70. For allowing the internal pressure of the vaporizing chamber 65 to take a predetermined value, the controller 70 controls an open/close degree of the flow rate control valve 71 mounted to the material supply passage 41 thereby controlling a to supply rate of hydrogen fluoride in such a manner that the internal pressure of the vaporizing chamber 65 shows a value within a given range. Like this, the fluid level of hydrogen fluoride is controlled in a given range.

Although, for adjusting the fluid level of hydrogen fluoride, either of the above-mentioned batch method and continuous method is usable, a feeding stability of hydrogen fluoride to the electrolytic tank 1 is easily affected by the internal pressure of the vaporizer 60. Accordingly, usage of the continuous method is preferable because it can keep the internal pressure of the vaporizer 60 at a given level and can continuously feed hydrogen fluoride to the tank while keeping the fluid level at a given level.

In case of usage of the continuous method by which hydrogen fluoride is continuously fed to the tank, it is preferable to employ an arrangement wherein a control means such as controller or the like is connected to the fluid level detecting means, and for the purpose of adjusting the amount of hydrogen fluoride supplied to the tank, with the aid of detected results of the fluid level detecting means, the open/close degree of the flow rate control valve 71 is controlled in such a manner that the fluid level of hydrogen fluoride in the vaporizer 60 is kept at a constant level.

The above-mentioned embodiment has the following effects.

In the above-mentioned construction, to the vaporizer 60, there is connected a fluid level detecting means that detects the fluid level of hydrogen fluoride in the vaporizer, and based on the detected results of the fluid level detecting means, the fluid level of hydrogen fluoride in the vaporizer 60 can be kept within a given range. Accordingly, controlling the fluid level of hydrogen fluoride in the vaporizer is facilitated, and thus, much stable feeding in amount of hydrogen fluoride to the electrolytic tank is to achieved.

Furthermore, in the above-mentioned construction, when, due to generation of a large amount of fluorine gas in the electrolytic tank, it becomes necessary to supply the electrolytic tank with a large amount of hydrogen fluoride, the difference between the internal pressure of the hydrogen fluoride supply source and that of the electrolytic tank does not induce a sudden fluctuation of the fluid level of the molten salt in the electrolytic tank and thus the electrolytic tank can supply fluorine gas stably.

Other Embodiments

In addition to the above-mentioned embodiment, the present invention has the other embodiment. In the other embodiment, as is shown in FIG. 3, the vaporizer 60 and the electrolytic tank 1 are installed in a common housing 80. In recent years, down-sizing has been required in the field of fluorine gas generating devices, and thus down-sizing is needed by facilities and equipments that are used for constituting the fluorine gas generating device.

In the other embodiment mentioned hereinabove wherein the vaporizer 60 and the electrolytic tank 1 are installed in the common housing 80, the fluorine gas generating device 100 can be reduced in size. Since, in this embodiment, the vaporizer 60 is received in the housing 80, the passage for feeding gaseous hydrogen fluoride can be reduced in length as compared with a passage used in a conventional fluorine gas generating device, and thus, liquefaction of hydrogen fluoride does not easily occur. Furthermore, since leakage of gaseous hydrogen fluoride to the outside can be suppressed, the device is assessed with an eye to its safety.

The present invention is not limited to the above-mentioned embodiments, and various modifications of the embodiments may to be carried out in light of the above-mentioned technical concept.

Although, in the foregoing description directed to the embodiments, it is described that the controller 70 (control means) is connected to the pressure detecting device 68 and a method for keeping the fluid level of hydrogen fluoride within a given range is described, it is of course possible to keep the fluid level of hydrogen fluoride within a given range by connecting a similar controller to the fluid level detecting device 69.

DESCRIPTION OF REFERENCE NUMERALS

-   -   100 . . . fluorine gas generating device     -   1 . . . electrolytic tank     -   2 . . . fluorine gas feeding system     -   3 . . . by-product processing system     -   4 . . . external device     -   5 . . . material supply system     -   7 . . . anode     -   8 . . . cathode     -   11 a . . . first gas chamber     -   12 a . . . second gas chamber     -   15 . . . first main passage     -   17 . . . first pump     -   20 . . . refining device     -   30 . . . second main passage     -   31 . . . second pump     -   60 . . . vaporizer     -   61 . . . hollow vessel     -   62 . . . hydrogen fluoride inlet portion     -   63 . . . hydrogen fluoride outlet portion 64 . . . temperature         adjusting device     -   65 . . . vaporizing chamber     -   66 . . . projected portions (fins)     -   67 . . . inserting tube     -   68 . . . pressure detecting device     -   69 . . . fluid level detecting device     -   70 . . . controller (control means)     -   71 . . . flow rate control valve     -   80 . . . housing 

1. A fluorine gas generating device that generates fluorine gas by subjecting hydrogen fluoride in a molten salt containing therein hydrogen fluoride to an electrolysis, which is characterized by an electrolytic tank that generates at an anode side a main-product containing as a main component fluorine gas and at a cathode side a by-product gas containing as a main component hydrogen gas by subjecting, in an electrolytic bath, hydrogen fluoride in a molten salt containing therein hydrogen fluoride to an electrolysis; a hydrogen fluoride supply source that stores therein hydrogen fluoride that is to be fed to the electrolytic tank to fill up hydrogen fluoride; a hydrogen fluoride supply passage through which hydrogen fluoride flows from the hydrogen fluoride supply source to the electrolytic tank; and, a vaporizer that is connected to the hydrogen fluoride supply passage to vaporize hydrogen fluoride supplied from the hydrogen fluoride supply source.
 2. A fluorine gas generating device as claimed in claim 1, in which the vaporizer comprises: a hollow vessel that is equipped with a temperature adjuster and has therein a vaporizing chamber; a hydrogen fluoride inlet portion that introduces thereinto liquefied hydrogen fluoride from the hydrogen fluoride supply source; and a hydrogen fluoride outlet portion that discharges gaseous hydrogen fluoride from the vaporizing chamber.
 3. A fluorine gas generating device as claimed in claim 1, further comprises: a flow rate control valve that controls a flow rate of hydrogen fluoride led into the vaporizer; a fluid level detecting means that detects a fluid level of hydrogen fluoride contained in the vaporizer; and a control means that, in accordance with a detected output from the fluid level detecting means, controls an open degree of the flow rate control valve in such a manner as to cause the fluid level of hydrogen fluoride in the vaporizer to take a given level.
 4. A fluorine gas generating device as claimed in claim 3, in which the control means is configured to control that hydrogen fluoride is fed into the vaporizer from the hydrogen fluoride supply source in such a manner the fluid level of liquefied hydrogen fluoride in the vaporizer constantly keeps a given level.
 5. A fluorine gas generating device as claimed in claim 1, in which the fluid level detecting means is either one of a pressure detecting device that detects a pressure in the vaporizer and a fluid level detecting device that detects the fluid level of hydrogen fluoride in the vaporizer.
 6. A fluorine gas generating device as claimed in claim 1, in which both the electrolytic tank and the vaporizer are installed in a common housing. 